1. Field of the Invention
The present invention relates to a field gas chromatograph with flame ionization for the analysis of a gaseous mixture of hydrocarbons extracted, in particular, from oil drilling mud. The mixture that is the object of analysis is made up of a fraction of heavy hydrocarbons (beyond pentane) dissolved in mud in gaseous form. There are many heavy hydrocarbons, in addition to the pentane, present in mud and dissolved in gaseous form in variable concentrations. Those of particular interest in relation to the present invention are preferably, but not exclusively, hexane, heptane, cyclohexane, methylcyclohexane, benzene and toluene.
2. Background of the Invention
A fraction of light gases from methane to pentane is commonly analysed via the use of various technologies, both in land oil drilling sites and offshore platforms. Only in recent times have services been introduced which offer the analysis of hydrocarbon gases beyond pentane, in oil drilling sites.
At the current state of the art, analysis of the concentration of a fraction of heavy hydrocarbon gaseous dissolved in drilling mud is carried out by gas chromatography coupled with mass spectrometry, or via gas chromatography combined with a detector which measures changes in thermal conductivity (thermal conductivity detector or TCD).
The use of a gas chromatograph-mass spectrometer combination involves the management of two separate instruments, one for the separation of gases over time along a chromatography column (gas chromatograph), the other for quantifying the concentration of a single gas species investigated in the sample of gas (mass spectrometry). The gas line is much more complex and difficult to manage this way. The spectrometer is also a very delicate instrument which is affected by environmental conditions. Its maintenance on site is in fact complex. Moreover, the use of a gas chromatography/mass spectrometry combination is made more complex by the fact that this type of measurement is affected by the presence of environmental gases, such as, among others, oxygen, nitrogen, CO, and CO2. This occurs because the spectrometer is not a selective analyser for hydrocarbons, but is able to detect the presence of any gas which generates ions of mass equal to that for which the analysis was programmed.
Also, in the case of the gas chromatography/TCD analysis combination, there is a problem of noise caused by the environmental gases. Although accurate instruments, TCD sensors are not selective for hydrocarbons. Since they are based on the reading of variations in the thermal conductivity of the gas analysed, TCD sensors in fact reveal the presence of all the gases in the sample, both hydrocarbons and environmental gases, or those from the drilling mud. Moreover, it is not possible to measure the sum of the hydrocarbons as a whole with the same type of TCD sensor with which the single hydrocarbons are analysed. Consequently, during analysis of the data, it is not possible to carry out a quality check by comparing the sum of the single hydrocarbon gaseous species and the analysis commonly known as total gas (total hydrocarbons).
The object of the present invention is, therefore, to provide an instrument which is able to analyse a gaseous mixture of hydrocarbons extracted, in particular, from oil drilling mud, and quantify a heavy fraction of gas thereof with accurate and precise measurements; while at the same time, provide an instrument that is easy to manage in remote land oil drilling sites and offshore platforms, even in difficult environmental conditions.
A second object of the present invention is to provide an instrument which is able to analyse a gaseous mixture of hydrocarbons extracted, in particular, from oil drilling mud, and quantify a heavy fraction of the gas present; while at the same time, provide an instrument that is able to perform a precise analysis in a continuous manner.
Another object of the present invention is to provide an instrument for the analysis of a gaseous mixture of hydrocarbons extracted, in particular, from oil drilling mud, and quantify a heavy gas fraction thereof; while at the same time, provide an instrument that is able to respond linearly both in the presence of concentrations of a few parts per million (ppm) and in the presence of a very high concentration of hydrocarbons in the gaseous mixture.